Conventionally various types of chip resistors have been proposed. For instance, the Patent Document 1 listed below discloses a chip resistor having a structure as shown in FIG. 9 of the present application. The Patent Documents 2 and 3 disclose a chip resistor having a structure as shown in FIG. 11 of the present application. It should be noted here that the chip resistor shown in FIG. 10 of the present application is not presented as prior art, but as a comparative example only for better understanding of the present invention.
Patent Document 1: JP-A-H11-273901
Patent Document 2: JP-A-2000-216001
Patent Document 3: JP-A-2002-203702
Specifically, the conventional chip resistor R1 shown in FIG. 9 of the present application includes a substrate A1, a resistor film A2 and a pair of terminal electrodes A3 connected to the resistor film A2. The substrate A1 has a predetermined length L and a predetermined width W. The resistor film A2 is formed with a trimming groove A4 for resistance adjustment.
In the chip resistor R1, the single resistor film A2 is provided between the paired terminal electrodes A3. With this arrangement, when a voltage is applied between the paired terminal electrodes A3, current flows only through the resistor film A2. Therefore, when the chip resistor R1 is applied to a circuit for high power supply, the temperature of the resistor film A2 may become excessively high. In such a case, the circuit may fail to operate properly.
This problem may be solved by employing the structure shown in FIG. 10, for example. Specifically, the chip resistor R2 shown in the figure includes a substrate B1, a plurality of resistor films B2 and a pair of terminal electrodes B3. The length L and the width W of the substrate B1 are equal to those of the above-described substrate A1. Each of the terminal electrodes B3 is formed on a longitudinally-extending side surface of the substrate B1. The resistor films B2 are connected in parallel with each other with respect to the paired electrodes B3. In the chip resistor R2 of this structure, the current flows as dispersed into the plurality of resistor films B2. Thus, although the size of the chip resistor R2 is the same as that of the chip resistor A, the rated power of the chip resistor R2 is large.
However, in the chip resistor R2, the effective length (length of the portion which functions as a resistor element) of each of the resistor films B2 is shorter than that of the resistor film A2 of the chip resistor R1. Therefore, when the chip resistor R2 has the application of a surge voltage, its resistance tends to vary significantly (meaning that the resistor has a low surge resistance).
With reference to FIG. 11 of the present application, the chip resistor disclosed in the Patent Document 2 or 3 will be described below. The chip resistor R3 shown in the figure includes a substrate 31, electrodes 32 and 33 formed on the substrate and a resistor element 34. The left end 37 of the resistor element 34 is connected to a projection 35 of the electrode 32, whereas the right end 38 of the resistor element 34 is connected to a projection 36 of the electrode 33. The resistor element 34 extends in a meandering manner between the two electrodes 32 and 33. With this arrangement, the current path in the resistor element 34 is longer than that of a resistor element extending straight between the two electrodes. Thus, the surge resistance of the chip resistor R3 is enhanced.
Further, by connecting the opposite ends of the resistor element 34 to the projections 35 and 36 of the electrodes 32 and 33, a sufficient distance is secured between the inner edge 32a of the electrode 32 and the outer edge 34a of the resistor film 34 (or between the inner edge 33a of the electrode 33 and the outer edge 34b of the resistor film 34). Thus, in forming the resistor element 34 and the electrodes 32 and 33 on the substrate 31 by screen printing, the resistor element 34 and the electrodes 32, 33 are prevented from becoming too close to or coming into contact with each other (if the resistor element and the electrodes are too close, discharge occurs between them).
However, the structure shown in FIG. 11 has the following drawbacks.
As described above, the electrodes 32 and 33 (and the resistor element 34) can be formed by screen printing. Specifically, a screen for printing formed with holes corresponding to the shape of the electrodes 32 and 33 is prepared. Then, the screen is placed on the upper surface of the substrate 31. Then, material paste is applied from the upper surface side of the screen. Then, the material paste is loaded into the holes for electrode formation by using a squeegee. Finally, the screen is removed from the substrate 31. In this way, the electrodes 32 and 33 are formed.
In the above-described process, however, in removing the screen from the substrate 31, part of the material paste loaded in the holes may be removed from the substrate 31 together with the screen. In such a case, the projections 35 and 36 of the electrodes 32 and 33 cannot have a desired straight edge but have a round edge as indicated by the double-dashed lines α and β in FIG. 11. As a result, the distance L0 between the two electrodes 32 and 33 is larger than the proper distance L, which causes the resistance of the chip resistor R3 to deviate from the desired value.